Effect Of Exercise On The Expression Of Leptin Receptor And The Activities Of Tissues Lipoidase Of Rats With Insulin Resistance

OBJECTIVES: OBJECTIVES: 1, To evaluate the serum level ofleptin, tissue levels of the expression of leptin receptor and the activity oflipoidase in rats with insulin resistance. 2, To explore the correlationbetween those subjects and insulin resistance. 3, To investigate thepossible mechanism why the exercise intervention could improve theinsulin resistance.METHODS: Forty-nine male Sprague-Dawley rats were randomlydivided into two groups: control group(n=9) and high fat dietgroup(n=40). After the rats had been fed with high-fat/high-sucrose dietfor six weeks, the serum level of fasting blood-glucose(FBG) and fastinginsulin(FINS) were measured and insulin sensitive index(ISI) wascalculated to confirm the establishment of insulin resistance(IR) model.Total thirty-four rats with IR were randomly assigned into four groups.â‘ model group(n=9), fed with high-fat/high-sucrose diet without anyintervention;â‘¡metformin group (n=8), fed with high-fat/high-sucrosediet and metformin (300mg/kg/d);â‘¢exercise group (n=9), fed withhigh-fat/high- sucrose diet and trained by swimming;â‘£exercise plus metformin group (n=8), fed with high-fat/high-sucrose diet andmetformin (300mg/kg/d), and in the same time trained by swimming.After twelve weeks' intervention, serum leptin was measured by theenzyme-linked immunoabsorbent assay; the expression of leptin receptorprotein in liver, skeletal muscle and adipose were measured byimmunohistochemistry, and the expression of leptin receptor mRNA inthe same tissues was measured by reverse transcriptase-polymerase chainreaction, the triglyceride content and the activities of lipoprotein lipaseand hepatic lipase in liver and skeletal muscle were measured bycolorimetric technique.RESULTS:â‘ six weeks after intervention with high-fat/high-sucrose diet, the levels of FBG, FINS were significant higher and ISIwas significant lower of the IR rats in model group than those of controlgroup (P<0.01 all)â‘¡twelve weeks after intervention, Compared withcontrol group, the serum leptin of the IR rats in model group wassignificantly higher (P<0.01), while the expression of leptin receptorprotein and receptor mRNA in liver, skeletal muscle and adipose werelower (P<0.01 all); the activities of lipoprotein lipase and hepatic lipasewere significantly lower and the triglyceride content was higher in liverand skeletal muscle (P<0.01 all). In correlation analysis, ISI correlatednegatively with leptin levels(r=-0.807,P=0.000), positively with theexpression of leptin receptor(r=0.776, P=0.002), the activity of lipoprotein lipase (r=0.528,P=0.017); and the triglyceride levelscorrelated positively with activity of lipoprotein lipase (r=-0.426,P=0.032). Six weeks after exercise for, compared with model group, thelevels of FBG and FINS and triglyceride of the IR rats in exercise group,metformin group and exercise plus metformin group were significantlylower (P<0.05 all), while the ISI was higher (P<0.05); the expression ofleptin receptor protein and leptin receptor mRNA in liver, skeletal muscleand adipose were higher; the triglyceride content in liver and skeletalmuscle was significantly lower and activities of lipoprotein lipase andhepatic lipase were significantly higher (P<0.05 all). Compared withmetformin group, the expression of leptin receptor protein and leptinreceptor mRNA in liver, adipose and skeletal muscle of the IR rats inexercise group were higher(P<0.05) and the triglycedde content in liverand skeletal muscle was lower and the activities of lipoprotein lipase andhepatic lipase were higherCONCLUSION:â‘ A rat model with insulin resistance could beestablished by fed high-fat/high-sucrose diet;â‘¡High serum leptin andlow-expression of leptin receptor protein and mRNA and lower activitiesof tissue lipoidase could be found in rats with insulin resistance.â‘¢Exercise can improve insulin resistance, the possible mechanisms mightbe: A. exercise lowers the serum leptin and increases the expression ofleptin receptor protein and mRNA; B. exercise decreases the triglyceride content and improves the activities of lipoprotein lipase and hepatic lipasein liver and skeletal muscle.